This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-241480, filed Aug. 9, 2000, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
This invention relates to an evaluation mask, a focus measuring method and an aberration measuring method that are used in the field of semiconductor technologies.
2. Description of the Related Art
As a design rules for semiconductor devices to be manufactured have been miniaturized in recent years, a focus margin of a lithography process have been reduced. Therefore, the specifications of a surface flatness of a wafer and a field curvature of exposure apparatus have become more and more rigorous. By the same token, high precision techniques have been required for focus measuring methods and field plane curvature measuring methods using a resist pattern transferred on the wafer.
Conventionally, the methods described in U.S. Pat. No. 4,908,656 (to be referred to as USP1) and U.S. Pat. No. 5,300,786 (to be referred to as USP2) are used as focus measuring methods using a resist pattern along with other methods realized by applying either or both of them.
With the USP1 method, a rhombic pattern formed on a mask is transferred onto a wafer and the focus is measured by using the phenomenon that the transferred pattern shows a maximal size at the best focus. Conventionally this method is called SMP.
With the USP2 method, on the other hand, a so-called Levenson type alternating phase shift mask is used to expose to light an isolated stripe type shield pattern that is designed to show a phase difference other than 180xc2x0 (optimally 90xc2x0) between the opposite ends thereof. Then, the image of the isolated stripe type shield pattern moves transversally when it is exposed to light at positive or negative defocus. The method utilizes this phenomenon for the purpose of measuring the focus.
The USP1 method can be applied not only to the focus measuring method of the isolated pattern but also a focus measuring method of a variety of periodic patterns. For example When the variety of periodic patterns includes two pairs of rhombic patterns which differ in size or two pairs of periodic patterns which intersect each other with an acute angle is formed by double exposures, the focus of the variety of periodic patterns can be measured by changing the period.
On the other hand, the USP2 method provides the advantage that the defocus with the proper (negative or positive) sign can be measured by a single exposure because the isolated stripe pattern moves substantially linearly relative to the best focal point.
A evaluation mask for evaluating a projection-type exposure apparatus, the mask according an aspect of the present invention comprises at least one diffraction grating pattern for producing a diffracted light of the positive first-order and a diffracted light of negative first-order, diffraction efficiencies of the diffracted lights being different respectively, one of the diffracted lights having a magnitude that is substantially zero, and an image of the at least one diffraction grating pattern being projected onto a test substrate or an image detector by the projection-type exposure apparatus; and
a reference pattern for obtaining a reference image to measure a displacement of the image of the at least one diffraction grating pattern, and an image of the reference pattern being projected onto the test substrate or the image detector by the projection-type exposure apparatus,
wherein the images of the at least one diffraction grating pattern and the reference pattern projected onto the test substrate or the image detector are used for evaluating the projection-type exposure apparatus.
A evaluation mask for evaluating a projection-type exposure apparatus, the mask according an aspect of the present invention comprises at least one diffraction grating pattern for producing a diffracted light of the positive first-order and a diffracted light of negative first-order, diffraction efficiencies of the diffracted lights being different respectively, one of the diffracted lights having a magnitude that is substantially zero, the at least one diffraction grating pattern comprising a light-shield section for shielding light and first and second transparent sections for transmitting light, the absolute value of the difference between a phase of light transmitted through the first transparent section and a phase of light transmitted through the second transparent section being 90xc2x0, and an image of the at least one diffraction grating pattern being projected onto a test substrate or an image detector by the projection-type exposure apparatus; and
a reference pattern for obtaining a reference image to measure a displacement of the image of the at least one diffraction grating pattern, and an image of the reference pattern being projected onto the test substrate or the image detector by the projection-type exposure apparatus,
wherein the images of the at least one diffraction grating pattern and the reference pattern projected onto the test substrate or the image detector are used for evaluating the projection-type exposure apparatus.
A focus measuring method for measuring a defocus of an image of a test mark formed on a focus test mark projected on a substrate, the image being projected by a projection-type exposure apparatus, the projection-type exposure apparatus projecting an image of a mask pattern formed in a photomask onto the substrate by way of a projection optical system comprises preparing an evaluation mask as the focus test mark, the evaluation mask comprising: at least one diffraction grating pattern for producing a diffracted light of the positive first-order and a diffracted light of negative first-order, diffraction efficiencies of the diffracted lights being different respectively, one of the diffracted lights having a magnitude that is substantially zero, and a reference pattern for obtaining a reference image to measure a displacement of the image of the at least one diffraction grating pattern,
preparing a substrate with a photo sensitizing material;
exposing the image of the diffraction grating pattern and the image of the reference pattern onto the substrate simultaneously, the diffraction grating pattern and the reference pattern comprising a test mark in the evaluation mask;
exposing an image of a trim pattern onto the substrate if the trim pattern exists in the evaluation mask; and
measuring the relative distance of the image of the diffraction grating pattern formed on the substrate and the image of the reference image formed on the substrate.
A focus measuring method for measuring a defocus of an image of a test mark formed on a focus test mark projected on a substrate, the image being projected by a projection-type exposure apparatus, the projection-type exposure apparatus projecting an image of a mask pattern formed in a photomask onto the substrate by way of a projection optical system comprises preparing an evaluation mask as the focus test mark, the evaluation mask comprising: at least one diffraction grating pattern for producing a diffracted light of the positive first-order and a diffracted light of negative first-order, diffraction efficiencies of the diffracted lights being different respectively, one of the diffracted lights having a magnitude that is substantially zero, and a reference pattern for obtaining a reference image to measure a displacement of the image of the at least one diffraction grating pattern; and
measuring the relative distance of the image of the diffraction grating pattern formed on the substrate and the image of the reference image formed on the substrate.
A focus measuring method for measuring a defocus of an image of a test mark formed on a focus test mark projected on a substrate, the image being projected by a projection-type exposure apparatus, the projection-type exposure apparatus projecting an image of a mask pattern formed in a photomask onto the substrate by way of a projection optical system comprises preparing an evaluation mask as the focus test mark, the evaluation mask comprising at least one diffraction grating pattern for producing a diffracted light of the positive first-order and a diffracted light of negative first-order, diffraction efficiencies of the diffracted lights being different respectively, one of the diffracted lights having a magnitude that is substantially zero, the at least one diffraction grating pattern comprising a light-shield section for shielding light and first and second transparent sections for transmitting light, the absolute value of the difference between a phase of light transmitted through the first transparent section and a phase of light transmitted through the second transparent section being 90xc2x0, and a reference pattern for obtaining a reference image to measure a displacement of the image of the at least one diffraction grating pattern; and
measuring the relative distance of the image of the diffraction grating pattern formed on the substrate and the image of the reference image formed on the substrate.
An aberration measuring method for measuring an aberration of a projection-type exposure apparatus based on a defocus of an image of a test mark formed on a focus test mark projected on a substrate, the image being projected by the projection-type exposure apparatus, the projection-type exposure apparatus projecting an image of a mask pattern formed in a photomask onto the substrate by way of a projection optical system comprises preparing an evaluation mask as the focus test mark, the evaluation mask comprising: at least one diffraction grating pattern for producing a diffracted light of the positive first-order and a diffracted light of negative first-order, diffraction efficiencies of the diffracted lights being different respectively, one of the diffracted lights having a magnitude that is substantially zero, and a reference pattern for obtaining a reference image to measure a displacement of the image of the at least one diffraction grating pattern,
preparing a substrate with a photo sensitizing material;
exposing the image of the diffraction grating pattern and the image of the reference pattern onto the substrate simultaneously, the diffraction grating pattern and the reference pattern comprising a test mark in the evaluation mask under the condition of
xcex/{NA(1xe2x88x92"sgr")}xe2x89xa6Pxe2x89xa62xe2x89xa6xcex/{NA(1+"sgr")}, 
where "sgr" is a partial coherence of a lighting optical system for lighting the test mark, P is a period of the image of the first pattern of the test mark, xcex is the wavelength of light of the lighting optical system and NA is a numerical aperture of the projection optical system;
exposing an image of a trim pattern onto the substrate if the trim pattern exists in the evaluation mask; and
measuring the relative distance of the image of the diffraction grating pattern formed on the substrate and the image of the reference image formed on the substrate.